1. Field of the Invention
The present invention generally relates to steady rests employed to rotatably support cylindrical workpieces. More specifically, this invention relates to a three-point, true centering steady rest having an integral displacement measuring device for remotely measuring the amount of material removed from a workpiece, and having a more efficient gripping action for assuring precision of the remote displacement measuring device.
2. Description of the Prior Art
Steady rests are commonly used in the machine tool industry to support cylindrical workpieces during machining or grinding operations when the operation is performed while the workpiece is rotating. There are primarily two benefits to using a steady rest under such conditions. The first is the prevention of deflection at the point of the operation when working with an elongated workpiece. The second is the stabilizing effect of the steady rest on the workpiece to improve the precision of the operation. Because of the precision operations for which a steady rest is typically employed, some means of gaging the diameter of the workpiece, or alternatively, gaging the amount of material removed from the workpiece, is necessary in conjunction with the steady rest.
Steady rests generally have at least two points of contact for supporting the workpiece and some form of adjustment for gripping the workpiece uniformly around its perimeter. A steady rest, such as that disclosed in U.S. Pat. No. 4,399,639 to Lessway, which is designed to grip the workpiece through its true center is therefore particularly desirable for its ability to accurately support the workpiece and for its ease of operation.
An improvement to the above true center action is disclosed in U.S. Pat. No. 4,650,237 to Lessway in which automatic three-point centering and gripping is accomplished. There, the gripping is provided by a center workpiece contact member and a pair of gripper arms, each having a side workpiece contact member. The gripper arms are operatively attached to an operator body slidably mounted within a housing. The center workpiece contact member is disposed on one end of the operator body adjacent and between the gripper arms. The gripping action of the gripper arms is accomplished by pentagonal cams which reside within a pair of cam tracks in the housing wall.
As the operator body is moved within the housing toward the workpiece, the gripper arms first move parallel with the operator body and to each other. Once alongside the workpiece, the gripper arms, in cooperation with the cam tracks, move laterally toward the workpiece in a manner which operatively provides centering and gripping engagement with the workpiece.
However, as noted above, steady rests typically require some means of gaging the workpiece to determine when the operation should be discontinued upon achieving a desired size on the workpiece. For purposes of precision, it is preferable to place the gage on the workpiece alongside the steady rest to gain the benefit of the workpiece's stability adjacent the steady rest. This requirement is a disadvantage with the prior art steady rests because of the limited space allowed in the vicinity of the steady rests, particularly when working with smaller workpieces, such as a camshaft or crankshaft. In addition, the machining and grinding debris and the increased possibilities of damage to the gage when adjacent the workpiece make this arrangement undesirable.
As can be appreciated from the above, it would be desirable to incorporate within the steady rest a means for gaging the workpiece during its machining operation. It would be additionally desirable if the gaging means could operate with the same precision as if it were directly gaging the workpiece without actually being in intimate contact with the workpiece.
Internal components of contemporary steady rest designs do not follow the workpiece precisely enough to sufficiently provide a surface from which to gage the workpiece. By example, U.S. Pat. No. 4,650,237 to Lessway, cited above, is limited by the pentagonal cam followers which inherently have higher frictional drag than is acceptable for the precision required.
Accordingly, what is needed is a steady rest having an integral means for gaging the workpiece during a precision operation in which the measuring device is positioned remotely from the workpiece without any significant loss in precision.